As a suppression control of occurrence of periodic disturbance, there are power system control in a power receiving and transforming facility, positioning control using a robot, axial torque resonance control for a dynamometer system, oscillation suppression of a motor casing (related to ride comfort of an electric vehicle, an elevator, or the like), and the like, and there is a demand for suppressing the periodic disturbance in the respective products with high accuracy.
For example, a motor generates a torque ripple by the principles of the motor, and this causes various problems such as oscillation, noise, an adverse effect on ride comfort, and electrical and mechanical resonance. Particularly, in a magnet embedded PM motor, a cogging torque ripple and a reluctance torque ripple are generated in a complex manner. As a countermeasure therefor, a periodic disturbance observer compensation method has been proposed as a control method of suppressing a torque ripple.
FIG. 8 illustrates a control block diagram regarding an n-th order torque ripple frequency component in a periodic disturbance observer which is disclosed in Patent Document 1 and Non-Patent Document 1.
A reference numeral 1 indicates a torque ripple compensation value calculation section. By multiplying differences between a control command rn (normally, 0) of a sine wave/a cosine wave and estimated values dTA^n, dTB^n by a periodic disturbance observer 3 by a sine wave value/a cosine wave value respectively then by adding these multiplication values, the torque ripple compensation value calculation section generates a torque ripple compensation command Tc*n, and outputs it to a control target (control object) 2. In the control target 2, periodic disturbance (hereinafter, referred to as periodic disturbance dTn) may occur. For example, if a control target (an object to be controlled) is a motor, a torque ripple which is disturbance synchronized with a rotation speed due to a cogging torque corresponds to the periodic disturbance, and causes oscillation or noise.
The periodic disturbance observer 3 is an observer that suppresses the periodic disturbance dTn. By using a system identification model in which disturbance is expressed in a complex vector for each frequency component as an inverse system model of the disturbance observer, the periodic disturbance observer 3 directly estimates the disturbance of frequency of the control target and compensates for the disturbance.
With this compensation, it is possible to achieve a high suppression effect regardless of orders of a target frequency, although a control configuration is relatively simple.
Regarding acquisition of a system identification model P^n, system identification is previously performed for a plant Pn (=PAn+jPBn) of a control target (a plant Pn (=PAn+jPBn) that is an object to be controlled) in advance of a control, and the model is expressed by Equation (1) in the form of a one-dimensional complex vector.P^n=P^An+jP^Bn  (1)
Here, the subscript n indicates an n-th order component, and any variable is a complex vector expressed as Xn=XAn+jXBn.
For example, in a case where system identification results from 1 Hz to 1000 Hz are expressed in a complex vector for each 1 Hz, a system can be expressed by using a table including 1000 one-dimensional complex vector elements. Alternatively, the system may be expressed by mathematical expression of the identification result. In either of these two methods, a system model for a specific frequency component can be expressed in a simple one-dimensional complex vector.
Here, not only the system identification model, but also P^n, rn, dTn, dT^n, and Tn mentioned in the above description are complex vectors expressed as Xn=XAn+jXBn.
Since a torque ripple of a motor is disturbance which is periodically generated according to a rotation phase θ [rad], as a control of the periodic disturbance observer 3, the periodic disturbance observer 3 performs conversion into a cosine coefficient TAn and a sine coefficient TBn of arbitrary order n (an integer multiple (or an integral multiple) of an electrical rotational frequency) by using torque pulsation frequency component extracting manner. Although there is Fourier transform etc. as an accurate measurement manner of a frequency component, simplicity is paramount in FIG. 8, and by causing plant output values to pass through low-pass filters GF(s) as one kind of simplification of the Fourier transform, a frequency component for suppression target of the periodic disturbance dTn is extracted. This extracted frequency component is multiplied by the inverse system expressed by the inverse number P^n−1 of the extracted system identification model, the periodic disturbance dTn is estimated on the basis of differences from the control command values having passed through the low-pass filters GF(s) and is outputted to the torque ripple compensation value calculation section 1 as a periodic disturbance estimated value dT^n (=dT^An+jdT^Bn), then the periodic disturbance dTn is suppressed by subtracting the estimated value from the control command rn.
Patent Document 1: International Publication No. WO2010/024195A1
Non-Patent Document 1: Torque Ripple Suppression Control Method based on Periodic Disturbance Observer with Complex Vector Representation for Permanent Magnet Synchronous Motors, IEEJ Journal of Industry Applications D, Vol. 132, No. 1, p. 84 to 93 (2012)